After the surprising success of its wireless AirPod earphones, Apple is planning to double down with bigger headphones. Apple is working on noise-cancelling, over-the-ear headphones with a release date aimed for the end of this year, Bloomberg reported Monday. Like the AirPods and the new smart home speaker HomePod, Apple is aiming the headphones to be priced for the high end of the market.

However, Apple reportedly has experienced development troubles and multiple redesigns for the headphones, says Bloomberg, so the headphones may be released later than the target date and could be scrapped altogether.

Apple's success with AirPods has given the Cupertino tech giant confidence to begin expanding its headphone product line. In the first seven months of 2017, the wireless headphone market sales increased by 22 percent compared to a year ago and Apple AirPods accounted for 85 percent of all wireless headphone dollar sales in the United States, according to research firm NPD Group.

"With a use case centering on frictionless access to Siri and other tasks initiated by voice, AirPods really act as an extension of the iPhone," wrote NPD Executive Director Ben Arnold in a August 2017 report. "Apple's path to leadership in the category is helped by disruptive pricing, brand resonance, and excitement over the W1 chip, which significantly eases Bluetooth connections to iOS and Mac devices."

Apple has not released AirPods' exact sales numbers; it has been lumped in with Apple Watch and other products in the "Other Sales" category. But that category has seen a 36 percent boost in revenue in the company's latest quarter, and Apple CEO Tim Cook praised the AirPods' success as "quite the cultural phenomenon" during his meeting with shareholders at Apple Park last month.

"They really are practically magic," Cook said, according to Business Insider. "The pairing is so seamless, and the fact that, as someone is talking to you, if you take one out the music will automatically stop, and if you replace it starts again. That is going quite well."

Apple's headphone ambitions put it in a collision course with already-popular brands such as Sony, Samsung -- and Apple's own Beats by Dre. Apple purchased Beats for $3 billion in 2014, and it remained Apple's main headphone brand until the introduction of AirPods. Because Beats sell at a broader price range, from $100 to $350, the new Apple headphones may not cannibalize Beats' margins, according to Bloomberg.